Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

931
FXUS63 KLOT 181821
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
121 PM CDT Sat Apr 18 2026

.KEY MESSAGES...

- Breezy and colder conditions through the weekend into early
  next week.

- Potential (20-40%) for some gusty showers Sunday afternoon.

- Frost/freeze conditions are expected many areas Sunday and
  especially Monday morning.

&&

.DISCUSSION...
Issued at 119 PM CDT Sat Apr 18 2026

A very cold upper trough (with 500 mb temperatures at an
impressive - 38C) will continue its trek across the Great Lakes
region tonight into Sunday. After the diurnal increase in cloud
cover, expect rapid clearing this evening. As mentioned for the
past few discussions, the northern periphery of a modest mid
1020s mb high will be centered southeast of the region across
the ArkLaTex, thus outside of a few outlying locations, we`ll
hold onto at least some surface flow through the night.
Additionally, there will be an increase in higher cloud cover
late tonight in the northwest the coldest temperatures are
forecast, but this would probably come in a little late to
prevent the temperature fall. While there are some factors that
would tend to limit the expansiveness of the frost threat, areas
of frost certainly may occur in more sheltered locations to
warrant a Frost Advisory tonight away from the urban core.

We will maintain the chances for showers on Sunday. A shortwave on
the back side of the upper trough will eventually get absorbed into
the bottom of the trough axis with time, however there will be a
period of moderately strong lower level forcing. Moisture is not
overlying plentiful, but cold temperatures aloft will support a
significant steepening of the low level lapse rates and lead to
scattered showers. The top of the cloud layer, while relatively
shallow, may get just close enough to the charge separation layer to
ring out a lightning strike or two, but the bulk of calibrated
thunder guidance from both the HREF/REFS suggest this would be
isolated. With the steep lapse rates, breezy conditions may be
augmented by any showers with a few gusts to 35 mph certainly
plausible.

There is much higher confidence in frost/freeze conditions on Sunday
night with a surface high to be in place overhead. There is the
potential with onshore flow that there could be some lower cloud
cover near the lake to keep things in check in both the IL/IN near
lakeshore areas.  A Freeze Watch will get hoisted to cover this.

There is also a strong ensemble signal for a bounce back to early
summer-like temperatures Tuesday through Thursday. The only fly in
the ointment for an overall nice mid week period will be on Tuesday.
Some guidance (mainly the GFS) squeezes out some showers--likely
under an incoming EML plume--ahead of a cold front Tuesday afternoon
and evening. Forecast soundings at this time look too capped for
thunderstorm development, although very steep lapse rates aloft
suggest we`ll need to keep an eye on this. CMC/EC ensemble suites
are not biting yet on this solution quite yet and few any members
wring out any precipitation.

Thereafter, a closed large upper low off the Pacific coast will
sweep through the Upper Midwest towards the end of the week. While
there are some uncertainties as to how this system will evolve, it
will send several synoptic shortwaves in our direction late week
through the weekend. The first will arrive in the Friday timeframe
with a robust cold front. This will bring the next thunderstorm
chances to the area late frame. 1" + PWAT values will accompany each
of these waves, and with potent forcing we may see some re-
aggravation of hydrologic issues during this time. Confidence is
also quite high that temperatures will drop back below normal.

KMD

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1213 PM CDT Sat Apr 18 2026

18Z Forecast Highlights:

- VFR cumulus cloud streets this afternoon through 00z.

- Breezy, 25-30 kt, westerly winds prevail through the afternoon
  then diminish this evening to less than 10kts overnight.

- Westerly winds increase Sunday morning, with a chance of
  sporadic showers throughout the region during the afternoon.

Post frontal overcast clouds continue to shift eastward across
northern Indiana, with development of diurnal cu cloud streets
across northern Illinois lasting through 00z. Breezy conditions
this afternoon, with westerly gusts in excess of 25-30kts will
continue to hold VFR ceilings in place. After 00z, winds
diminish below 10kts heading into the overnight, with skies
clearing throughout the forecast area.

Another disturbance will dive into the Midwest on Sunday,
leading to another increase in west-northwest winds and bringing
the potential for sporadic showers across northern Illinois
into northern Indiana.

Baker/KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory from midnight tonight to 9 AM CDT Sunday for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ106-ILZ107-ILZ108.

     Freeze Watch from late Sunday night through Monday morning for
     ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-
     ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
     ILZ103-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Frost Advisory from midnight CDT /1 AM EDT/ tonight to 9 AM
     CDT /10 AM EDT/ Sunday for INZ001-INZ002-INZ010-INZ011-
     INZ019.

     Freeze Watch from late Sunday night through Monday morning for
     INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Small Craft Advisory until 10 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

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